I don't know how you out-pressure it, the 3/6 guy is a brick wall that stops even a turn 5 offense. Priestess gives the 4 + 1 damage spell, or twins, or comet, something that helps you depending on where you at in the game. Leona delays the turn, and then 5/5 daddy. Sometimes you also get the 1-drop 3/3, so... don't know what kind of things you need to spawn to beat Daybreak early. I am 6, 7, 6 using Targon this week.
Fighting for board vs Targon is easy in Expeditions. Their early game followers are either vanilla 2/2s and 3/2s or even worse statted invoke cards. You always let them hit you in the face with the beefy Daybreak dudes. Targon has no burn, so it's really not a big deal. You are not afraid to take advantageous trades because they have no 1 dmg ping. No, the 5m 4/1 spell does not count as efficient removal and is not something you should account for the earlygame. You will get ahead early with your superior followers and always open attack on t4 onwards if they have Leona in the deck.
The flow is simple. On their attack turn: if you are already ahead on tempo, they are forced to play a card. If they pass, you can develop if that will snowball you the win or you can pass and open attack if you have enough stats on the board to run over theirs. Honestly, their only way to punish your develop is with those two Celestial removal spells or Sunburst, but guess what, they spend just as much mana (OR MORE) on the spell as you did on the unit. Targon's weakness is that their only units worth a damn cost 4m or more. Which means they either tap out of any Celestial removal so you're safe to dump your mana on bigger units OR they play more shit stat minions that are good for one turn only, which you can pretty much ignore. Take a "gamechanger" card like Leona. She's usually tapping them out in the midgame to play. If you open attack, she does nothing on play. If she is played on their attack turn, she only represents 3 face damage. Let her have it.
On your attack turn: Open attack open attack open attack. There are no burst or fast Daybreak cards and their only combat trick is Pale Cascade, which is only a +1 hp buff, robs them of the Nightfall effect AND denies them their own Daybreak for the turn. I know it's easy to just say open attack, but that's why making sure your board is advantageous at the end of their turn is so important.
The 4/1 spell is honestly not even that good. How many units are core build arounds that die to 4 damage, but not 3? I can think of Maokai and Neverglade. And they paid 5m for it. And they pass initiative for it. Plus they played a 3m 1/2 to draw it. AND spells are reactionary, so a 5m spell should have WAY more value than trading pretty evenly. With this style of play, the Sisters is the only card that I am hard pressed to have an answer for.
Playing against Targon is kind of the opposite of playing against Bilgewater, but that makes it counter-intuitive for some people. Against Bilgewater, sometimes you're willing to take unfavorable trades if it means protecting your face from plunder effects. Against Targon, you are fully free to use your health as a resource to make sure you only take the most favorable trades against their weak/vanilla followers. Targon is also way too "honest" of a region, making you pretty confident of your trading on defense, only needing to account for +1HP buffs most of the time.
In my last three 7-win runs, I used Shadow Isles for Fearsome to ignore their units twice and Noxus to just value trade them repeatedly. My last SI deck was honestly a mish mash of Fearsome and removal, with two Nocturnes that were the ONLY Nightfall cards in the deck. I lost every non-Targon matchup because the deck was hot garbo. But it worked against Targon because I was able to go face on my turns and trade my 1m 2/1 for up to their 3m units on defense.
I can see Demacia and Freljord working for the same reasons as Noxus, eking out those value trades. I can see PZ having trouble since you DON'T want to trade removal for their units 1-1, you want to force favorable trades always. Same for Bilgewater to a lesser extent and same goes for Ionia if you're not doing elusives.